Effect of surfactant on the electrodeposition of Ni-P coating in emulsified supercritical CO₂ baths

The electrodeposition behavior and material properties of the Ni-P alloy coatings produced in emulsified supercritical CO₂ (sc-CO₂) bath with different surfactants (dodecyl octaethylene glycol ether (C ₁₂EO₈) and a commercial fluorosurfactant) were investigated. The formation of holes or voids which is normally found in conventional aqueous coating could be avoided if the electrodeposition was conducted in the emulsified sc-CO₂ bath with proper addition of surfactant, but with the sacrifice of current efficiency. At a lower concentration of surfactant addition, the experimental results showed that fluorosurfactant was more effective than C₁₂EO₈ in reducing the surface roughness and void formation in the coating. A significant increase in micro-hardness of the Ni-P coating was observed if it was electrodeposited in the emulsified sc-CO₂ bath as compared with that formed at conventional aqueous bath. The wear rate of the Ni-P coating formed in the emulsified sc-CO₂ bath was relatively lower with fluorosurfactant as the surfactant than that with C₁₂EO₈.